1. Field of the Invention
The invention relates to a wheel support device.
2. Description of the Related Art
In order to support a wheel such that the wheel is rotatable with respect to a suspension provided on a body of a vehicle, for example, a wheel support device shown in FIG. 4 is used. The wheel support device includes a hub unit 80 and a joint 90 that transmits torque to the hub unit 80.
The hub unit 80 includes a fixed ring 81, a rotary ring 82, and rolling elements 83. Internal splines 84 are formed in the inner periphery of the rotary ring 82. The fixed ring 81 is fixed to the suspension. The wheel is connected to the rotary ring 82. The rolling elements 83 are arranged between the fixed ring 81 and the rotary ring 82. The joint 90 has an outer ring 89. The outer ring 89 has a tubular body portion 88 and a shaft portion 87. The shaft portion 87 extends from the body portion 88 in the axial direction. External splines 86 that mesh with the internal splines 84 are formed on the outer periphery of the shaft portion 87 so that torque transmission between the hub unit 80 and the joint 90 is allowed.
When the configuration shown in FIG. 4 is employed, many processes are required to assemble the hub unit 80 and the joint 90 together. That is, the following processes are required. First, an alignment for positioning the hub unit 80 and the outer ring 89 of the joint 90 such that the hub unit 80 and the outer ring 89 extend along the same straight line is performed (first process). The shaft portion 87 of the joint 90 is press-fitted (temporarily press-fitted) into the rotary ring 82, and the distal end of the shaft portion 87 is protruded from an axial end face (left end face in FIG. 4) of the rotary ring 82 (second process). A temporary nut (not shown) is screwed to a threaded portion 87a formed at the distal end of the shaft portion 87 (third process). By screwing the temporary nut to the threaded portion 87a, the shaft portion 87 is press-fitted (fully press-fitted) into the rotary ring 82 until no gap remains between the rotary ring 82 of the hub unit 80 and the outer ring 89 of the joint 90 (fourth process). The temporary nut is removed from the shaft portion 87 (fifth process). A nut 85 is fastened to the threaded portion 87a of the shaft portion 87 (sixth process). The nut 85 is fixed to the axial end face of the rotary ring 82 by crimping, or the like, to prevent loosening of the nut 85 (seventh process). As shown in FIG. 4, the shaft portion 87 is press-fitted into the rotary ring 82 so that the external splines 86 that extend in the axial direction mesh with the internal splines 84 that extend in the axial direction. Therefore, particularly strict dimensional control is required to form the splines 86, 84. As a result, many man-hours are required also in the process of forming the splines.
Therefore, in order to make it easier to assemble a hub unit and a joint together, for example, a wheel support device (wheel bearing device) described in Japanese Patent Application Publication No. 2008-284920 (JP 2008-284920 A) (see FIG. 4) is used. In the wheel support device, first splines are formed in an annular side face of a rotary ring of the hub unit, the annular side face being on one side of the rotary ring in the axial direction. In addition, second splines that mesh with the first splines are formed in an annular side face of an outer ring of the joint, the annular side face being on the other side of the outer ring in the axial direction. The first splines are formed in substantially the entirety of the annular side face of the rotary ring. The second splines are formed in substantially the entirety of the annular side face of the outer ring.
In the case of the wheel support device described in JP 2008-284920 A (see FIG. 4), the hub unit and the joint are assembled together in the following manner. First, the hub unit and the outer ring of the joint are arranged so as to face each other in the axial direction. Then, the first splines of the hub unit and the second splines of the joint are meshed with each other. After that, the hub unit and the outer ring of the joint are fastened together with a bolt.
As described above, in the case of the wheel support device described in JP 2008-284920 A (see FIG. 4), it is easy to assemble the hub unit and the joint together. However, as described above, the first splines and the second splines are formed in substantially the entirety of the corresponding annular side faces. Therefore, in order to form the first and second splines through plastic working with the use of, for example, a press, a large pressing load is required. In addition, in order to accurately form the entirety of the splines, a high-level working technique is required. Therefore, for example, there is a wheel support device in which splines are formed only in an outer peripheral region of an annular side face of a rotary ring of a hub unit, the annular side face being on one side of the rotary ring in the axial direction (for example, see Japanese Patent Application Publication No. 2008-174178 (JP 2008-174178 A) (see FIG. 3)).
In the hub unit described in JP 2008-174178 A (see FIG. 3), splines need to be formed only in the outer peripheral region of the annular side face. Therefore, a press load that is required to form the splines through plastic working with the use of, for example, a press is smaller than that in the case of the hub unit described in JP 2008-284920 A (see FIG. 4). Therefore, it is easier to accurately form the splines than in the case of the hub unit described in JP 2008-284920 A.
However, in the case where the splines are formed only in part of the annular side face, contact pressure that acts on the splines may increase as transmission torque increases. That is, in the case where the splines are formed in part of the annular side face, the magnitude of torque that is transmitted between the joint and the hub unit may be limited.